Historically, computer systems have each included their own storage within the computer system enclosure, or chassis, or “box.” A typical computer system included a hard disk, such as an IDE or SCSI disk, directly attached to a disk controller, which was in turn connected to the motherboard by a local bus. This model is commonly referred to as direct attached storage (DAS).
However, this model has certain disadvantages in an enterprise, such as a business or university, in which many computers are networked together, each having its own DAS. One potential disadvantage is the inefficient use of the storage devices. Each computer may only use a relatively small percentage of the space on its disk drive with the remainder of the space being wasted. A second potential disadvantage is the difficulty of managing the storage devices for the potentially many computers in the network. A third potential disadvantage is that the DAS model does not facilitate applications in which the various users of the network need to access a common large set of data, such as a database. These disadvantages, among others, have caused a trend toward more centralized, shared storage in computer networks.
Initially the solution was to employ centralized servers, such as file servers, which included large amounts of storage shared by the various workstations in the network. That is, each server had its own DAS that was shared by the other computers in the network. The centralized server DAS could be managed more easily by network administrators since it presented a single set of storage to manage, rather than many smaller storage sets on each of the individual workstations. Additionally, the network administrators could monitor the amount of storage space needed and incrementally add storage devices on the server DAS on an as-needed basis, thereby more efficiently using storage device space. Furthermore, because the data was centralized, all the users of the network who needed to access a database, for example, could do so without overloading one user's computer.
However, a concurrent trend was toward a proliferation of servers. Today, many enterprises include multiple servers, such as a file server, a print server, an email server, a web server, a database server, etc., and potentially multiple of each of these types of servers. Consequently, the same types of problems that existed with the workstation DAS model existed again with the server DAS model.
Network attached storage (NAS) and storage area network (SAN) models were developed to address this problem. In a NAS/SAN model, a storage controller that controls storage devices (typically representing a large amount of storage) exists as a distinct entity on a network, such as an Ethernet or FibreChannel network, that is accessed by each of the servers in the enterprise. That is, the servers share the storage controlled by the storage controller over the network. In the NAS model, the storage controller presents the storage at a filesystem level, whereas in the SAN model, the storage controller presents the storage at a block level, such as in the SCSI block level protocol. The NAS/SAN model provides similar solutions to the fileserver DAS model problems that the fileserver DAS model provided to the workstation DAS problems. In the NAS/SAN model, the storage controllers have their own enclosures, or chassis, or boxes, discrete from the server boxes. Each chassis provides its own power and cooling, and since the chassis are discrete, they require networking cables to connect them, such as Ethernet or FibreChannel cables.
Another recent trend is toward storage application servers. In a common NAS/SAN model, one or more storage application servers resides in the network between the storage controller and the other servers, and executes storage software applications that provide value-added storage functions that benefit all of the servers accessing the common storage controller. These storage applications are also commonly referred to as “middleware.” Examples of middleware include data backup, remote mirroring, data snapshot, storage virtualization, data replication, hierarchical storage management (HSM), data content caching, data storage provisioning, and file service applications. The storage application servers provide a valuable function; however, they introduce yet another set of discrete separately powered and cooled boxes that must be managed, require additional space and cost, and introduce additional cabling in the network.
Therefore, what is needed is a way to improve the reliability and manageability and reduce the cost and physical space of a NAS/SAN system. It is also desirable to obtain these improvements in a manner that capitalizes on the use of existing software to minimize the amount of software development necessary, thereby achieving improved time to market and a reduction in development cost and resources.